In signal processing, the Nyquist frequency (or folding frequency), named after Harry Nyquist, is a characteristic of a sampler, which converts a continuous function or signal into a discrete sequence. In units of cycles per second (Hz), its value is one-half of the sampling rate (samples per second).
Q. Why do we sample a signal?
To convert a signal from continuous time to discrete time, a process called sampling is used. The value of the signal is measured at certain intervals in time. If the signal contains high frequency components, we will need to sample at a higher rate to avoid losing information that is in the signal.
Table of Contents
- Q. Why do we sample a signal?
- Q. What is the Nyquist rule?
- Q. How do you calculate aliased frequency?
- Q. Which circuit is used for obtaining ideal sampling signal?
- Q. What is the difference between natural and flat top sampling?
- Q. In which technique noise interference is maximum?
- Q. What is meant by Flat Top sampling?
- Q. Which is better natural sampling or flat topped sampling and why?
Q. What is the Nyquist rule?
Nyquist’s theorem states that a periodic signal must be sampled at more than twice the highest frequency component of the signal. In practice, because of the finite time available, a sample rate somewhat higher than this is necessary. A sample rate of 4 per cycle at oscilloscope bandwidth would be typical.
Q. How do you calculate aliased frequency?
For example if the signal is of f=21Hz and is sampled with fs=10Hz, then the resulting (aliased) frequency would be |n∗fs−f|=|2∗10−21|=1Hz.
Q. Which circuit is used for obtaining ideal sampling signal?
Zero-order hold circuit.
Q. What is the difference between natural and flat top sampling?
The difference between natural sampling and flat top sampling is that: In natural sampling the analog input is multiplied by a train of uniformly spaced, rectangular pulses. While in flat top sampling the top of the samples are flat, this means they have a constant amplitude.
Q. In which technique noise interference is maximum?
In PAM, the amplitude of the rectangular pulse train is varied according to the instantaneous value of the modulating signal. Due to this, the required power for transmission is also varied. Due to varying amplitude of carrier, the interference of noise is very high in PAM.
Q. What is meant by Flat Top sampling?
Flat Top Sampling During transmission, noise is introduced at top of the transmission pulse which can be easily removed if the pulse is in the form of flat top. Here, the top of the samples are flat i.e. they have constant amplitude. Hence, it is called as flat top sampling or practical sampling.
Q. Which is better natural sampling or flat topped sampling and why?
With the help of hold and sample circuit ‘flat top sampling’ is done. In flat top sampling the top of samples are constant and are equal to instantaneous value of the signal while a more practical method of sampling is natural sampling in which the width of pulse is finite.
